1. Field of the Invention
The invention relates to thermal insulation with a double walled housing in which the space between the housing walls is evacuated and filled with insulating material and feedthroughs are provided between the interior of the housing and the outer area.
2. Description of the Prior Art
Such thermal insulation is used in power engineering in apparatus in which the loss of heat is to be avoided. Thermal insulation is used primarily in high-temperature storage batteries of the alkali metal and chalcogen type which must be surrounded by heat-retarding material in order to prevent the storage cells from cooling off particularly in the operating pauses.
German Offenlegungsschrift DE-OS 32 47 968 discloses thermal insulation around a high-temperature storage battery. The thermal insulation is bounded on the inside and outside by a double-walled housing. Between the walls of the housing is an evacuated space which is filled with insulating material retarding the heat flux. The opening of the housing which exposes the interior of the thermal insulation, is closed off by a plug. The plug likewise has two walls with insulating material arranged between its housing walls. Feedthroughs go through the plug and cooling lines and electrical leads are brought through the feedthroughs.
A disadvantage of this thermal insulation is that there is a very large heat loss in the vicinity of the plug. This happens because the plug material does not have a large heat conduction coefficient and no high mechanical strength. The plug further has no flexible circular surface for sealing the interior airtight. A further disadvantage are the feedthroughs in the vicinity of the plug which cause a large heat loss.